According to the four-page document, FBI officials used allegations from a dossier funded in part by Hillary Clinton’s campaign to convince a FISA court judge to approve a warrant on Trump adviser Carter Page. Democrats have claimed the memo is misleading and lacking context, while some Republicans have asserted that it represents an unprecedented abuse of power by FBI agents biased against Trump.

The memo is short, but it throws out a lot of names, dates, and details. With politically-charged accusations flying back and forth over classified material the public may never see, these are some of the players you may need to be familiar with to try to make sense of all this:

Rep. Devin Nunes

Rep. Devin Nunes, R-Calif., the chairman of the House Intelligence Committee and a former member of President Trump’s transition team, has faced scrutiny before over his relationship with the White House. Last year, he worked with administration officials to spread allegations that the Obama administration improperly unmasked Americans picked up in surveillance of foreign agents. At the time, he faced an ethics investigation for allegedly disclosing classified information to the media, but the case was closed in December. Though he recused himself from the committee’s investigation of Russian interference in the 2016 election during the ethics probe, Nunes remained involved in reviewing and approving subpoena requests. Members of the Republican committee staff compiled the memo for him.

Rep. Adam Schiff

Rep. Adam Schiff, D-Calif., the ranking Democrat on the House Intelligence Committee, has become a frequent presence on cable news disputing claims made by Nunes or the White House over the last year. Schiff, one of two members of the committee who viewed the classified intelligence related to the Carter Page FISA warrants, has fought in the last two weeks to keep the Republican memo from seeing the light of day, citing concerns about its accuracy and its national security implications. When the push to release it picked up steam, his staff compiled a 10-page memo rebutting its claims. The committee has not yet released the Democratic memo, but Republicans say it will be made public once it completes the same review process theirs did.

Carter Page

An unlikely figure to be at the center of the battle over the credibility of the entire Russia investigation, Carter Page was a somewhat obscure foreign policy adviser to then-candidate Donald Trump. Page has testified that he never met or spoke to Trump and did not attend the one meeting the foreign policy team held, but records do show he had email contact with campaign aides through the summer of 2016. Page had business ties to Russia and was questioned by the FBI in a 2013 counterintelligence investigation of a Russian operative who tried to recruit him as an asset. A trip he made to Moscow in July 2016 drew investigators’ interest. A FISA warrant was obtained for him in October and renewed three times over the following year. The dossier alleged that Page met with a Russian intelligence official and the CEO of a government-linked oil company while in Moscow and discussed ending economic sanctions. Those claims have never been publicly verified, and Page has adamantly denied them in media interviews.

Christopher Steele

Christopher Steele is a former British intelligence officer who the FBI had considered a credible source in past cases. He was hired by Fusion GPS, a research firm being paid by Hillary Clinton’s campaign and the Democratic National Committee, to investigate Trump’s ties with Russia. He compiled several memos between June and October 2016. That dossier of information is what Republicans allege formed the basis for the FBI’s surveillance of Page. Steele has said that he was so alarmed by what he learned in his investigation of Trump that he went to the FBI in July 2016 and he continued sharing information with them until October. According to the memo, the FBI terminated its relationship with Steele after learning he briefed reporters on his findings and an independent unit concluded his claims were only “minimally corroborated.” Republicans on the Senate Judiciary Committee have submitted a criminal referral to the DOJ alleging that he lied to FBI agents about his contacts with the media.

James Comey

President Trump fired FBI Director James Comey in May 2017, ostensibly because Comey treated Hillary Clinton unfairly in the investigation of her use of a private email server as secretary of state. In an interview with NBC, though, Trump suggested Comey’s unwillingness to drop the Russia investigation led to his firing. Comey allowed a friend to leak details of his conversations with Trump to the press, and he testified before Congress that he did so in the hope that a special counsel would be appointed to take over the probe of Russian interference. According to the memo, Comey was one of the senior officials who signed off on FISA applications for Page that Republicans claim omitted key facts about Steele’s partisan motivation.

Andrew McCabe

Then-Deputy FBI Director Andrew McCabe also approved at least one application for a FISA warrant on Page. McCabe resigned abruptly earlier this week amid reports that the DOJ inspector general is questioning his handling of certain decisions in the Clinton email investigation. McCabe had also been targeted by Trump on Twitter because his wife received donations from Virginia Gov. Terry McAuliffe for her failed state Senate run in 2015 and McAuliffe is a close ally of the Clintons. According to the memo, McCabe told the intelligence committee the warrant on Page would not have been sought without the dossier. Democrats say that is a mischaracterization of his testimony.

Dana Boente

Recently chosen as FBI general counsel, Dana Boente had served as a federal prosecutor in Virginia and head of the DOJ’s national security division. In his role as acting deputy attorney general, he temporarily oversaw the FBI’s Russia probe after Attorney General Jeff Sessions recused himself. According to the memo, he signed off on at least one FISA application for Page.

Sally Yates

Sally Yates was acting attorney general for the first ten days of Trump’s presidency, ultimately fired for refusing to enforce his travel ban executive order. Prior to that, she had worked as a federal prosecutor and a deputy attorney general under the Obama administration. Yates also approved at least one warrant application targeting Page.

Rod Rosenstein

Deputy Attorney General Rod Rosenstein signed one or more FISA application for Page. At Trump’s request, he authored a memo recommending Comey’s firing, and he was the one who later appointed Robert Mueller as special counsel. Rosenstein and FBI Director Christopher Wray went to the White House earlier this week to advocate against releasing the Nunes memo. Asked Friday whether he still has confidence in Rosenstein after reading the memo, Trump said, “You figure that one out.”

Bruce Ohr

After the election, senior DOJ official Bruce Ohr was interviewed by investigators about his communications with Steele. According to the memo, he revealed that Steele told him in September 2016 that “desperate” to prevent Trump from being elected. Republicans say that bias was not reflected in the FISA applications. Ohr’s wife also worked for Fusion GPS and the memo states he provided the FBI with all of her opposition research on Trump. Ohr was reportedly demoted after those details were revealed.

George Papadopoulos

The memo appears to verify New York Times reporting that information on another Trump foreign policy adviser, George Papadopoulos, was the catalyst for the counterintelligence probe in July 2016. He reportedly told an Australian diplomat that Russia had copies of thousands of emails that would embarrass Clinton, and that diplomat went to the FBI once hacked Democratic emails started appearing online. Papadopoulos has admitted to lying to the FBI about his contacts with Russians.

Peter Strzok

The memo notes that the Papadopoulos investigation was opened by FBI Agent Peter Strzok. In text messages exchanged with his mistress, a DOJ attorney, around the same time, he expressed disdain for Trump and spoke of an unspecified “insurance policy” in case Trump was elected. Strzok initially served on Mueller’s team, but he was removed when the DOJ inspector general uncovered the texts. He also played a significant role in the Clinton investigation, including working on a draft of the letter Comey sent to Congress announcing that the probe was being reopened 10 days before the election.

Robert Mueller

Former FBI Director Robert Mueller was appointed as special counsel in May 2017 with the purpose of investigating Russian efforts to interfere in the 2016 election and any possible ties between the Trump campaign and Russia. The investigation has resulted in guilty pleas by Papadopoulos and former National Security Adviser Michael Flynn for making false statements and the indictment of two campaign officials for money laundering unrelated to their work for Trump. He reportedly wants to speak to Trump directly, something the president has indicated willingness to do, but his attorneys have not decided if they will allow it. Some Trump allies have called for Mueller’s investigation to be shut down, and such demands will likely increase in the wake of the memo’s release.

Christopher Wray

After firing Comey, Trump appointed Christopher Wray as FBI director. He had previously served as an assistant U.S. attorney and head of the DOJ’s criminal division before going into private practice. At the time, Trump described him as “a man of impeccable credentials.” In recent tweets, though, the president has questioned the integrity of FBI and DOJ leadership. Wray opposed the release of the Nunes memo, and the FBI issued a statement saying it had “grave concerns” due to “material omissions” in the document.